Common demulsifiers

The commonly used nonionic demulsifiers in oil fields are mainly as follows:

1. SP type demulsifier

The main component of SP-type demulsifier is polyoxyethylene polyoxypropylene octadecyl alcohol ether, with the theoretical structural formula R(PO)x(EO)y(PO)zH, where: EO – polyoxyethylene; PO – polyoxypropylene; R – fatty alcohol; x, y, z – degree of polymerization. SP-type demulsifier appears as a pale yellow paste with an HLB value of 10-12 and is soluble in water. SP-type nonionic demulsifier has a good demulsifying effect on paraffinic crude oil. Its hydrophobic portion consists of carbon 12-18 hydrocarbon chains, and its hydrophilic groups achieve hydrophilicity by forming hydrogen bonds with water through the interaction of hydroxyl (-OH) and ether (-O-) groups in the molecule. Because the hydrophilicity of hydroxyl and ether groups is relatively weak, one or two hydroxyl or ether groups are insufficient to pull the hydrophobic groups of the carbon 12-18 hydrocarbon chains into water; multiple such hydrophilic groups are required to achieve water solubility. The larger the molecular weight and the longer the molecular chain of a nonionic demulsifier, the more hydroxyl and ether groups it contains, resulting in greater tensile strength and stronger demulsification ability for crude oil emulsions. Another reason SP-type demulsifiers are suitable for paraffinic crude oils is that paraffinic crude oils contain little or no gums and asphaltenes, have fewer lipophilic surfactants, and a lower relative density. For crude oils with high gum and asphaltenes content (or a water content greater than 20%), SP-type demulsifiers have weaker demulsification ability because of their simple molecular structure, lacking branched and aromatic structures.

2. AP type demulsifier

AP-type demulsifier is a polyoxyethylene polyoxypropylene polyether with polyethylene polyamine as the initiator. It is a multi-branched nonionic surfactant with the molecular structure: D(PO)x(EO)y(PO)zH, where: EO-polyoxyethylene; PO-polyoxypropylene; R-fatty alcohol; D-polyethylene polyamine; x, y, z-degree of polymerization.

AP-type demulsifiers are more effective than SP-type demulsifiers for demulsifying paraffinic crude oil emulsions. They are more suitable for demulsifying crude oils with a water content higher than 20% and can achieve rapid demulsification at low temperatures. For example, if SP-type demulsifiers settle and demulsify within 2 hours at 55-60℃, AP-type demulsifiers only need to settle and demulsify within 1.5 hours at 45-50℃. This is due to the structural characteristics of AP-type demulsifier molecules. The initiator, polyethylene polyamine, determines the molecular structure: long molecular chains with many branches, resulting in higher hydrophilicity than the simpler SP-type demulsifier. The multi-branched characteristic gives AP-type demulsifiers higher wetting and penetrating properties. When demulsifying crude oil emulsions, AP-type demulsifier molecules can quickly penetrate the oil-water interface film, occupying a larger surface area than the upright monolayer arrangement of SP-type demulsifier molecules. Therefore, a smaller dosage is required, resulting in a more significant demulsification effect. Currently, this type of demulsifier is the best-used non-ionic demulsifier in Daqing Oilfield.

3. AE type demulsifier

AE-type demulsifiers are polyoxyethylene and polyoxypropylene polyethers initiated by polyethylene polyamines, and are a type of branched nonionic surfactant. Unlike AP-type demulsifiers, AE-type demulsifiers are two-stage polymers with smaller molecules and shorter branches. The molecular structure is: D(PO)x(EO)yH, where: EO – polyoxyethylene; PO – polyoxypropylene; D – polyethylene polyamine; x, y – degree of polymerization. Although the molecular appearance of AE-type and AP-type demulsifiers differs significantly, their molecular composition is the same; the differences lie only in the monomer dosage and polymerization sequence.

(1) When designing and synthesizing two nonionic demulsifiers, the amount of materials used at the head and tail are different, and the length of the polymer molecules produced is also different.

(2) AP type demulsifier molecules are two-stage, using polyethylene polyamine as an initiator to polymerize with polyoxyethylene and polyoxypropylene to form block copolymers; AE type demulsifier molecules are two-stage, using polyethylene polyamine as an initiator to polymerize with polyoxyethylene and polyoxypropylene to form two-stage copolymers. Therefore, the designed AP type demulsifier molecules should be longer than the AE type demulsifier molecules.

AE type is a two-stage, multi-branched crude oil demulsifier, also suitable for demulsifying asphalt-based crude oil emulsions. The higher the content of lipophilic surfactants in asphalt-based crude oil, the stronger the viscosity, the smaller the oil-water density difference, and the more difficult it is to demulsify. However, AE type demulsifiers offer rapid demulsification. Furthermore, AE type demulsifiers are also excellent anti-waxing and viscosity-reducing agents. Due to its multi-branched molecular structure, it readily forms micro-networks, causing existing paraffin single crystals in the crude oil to fall into these networks. This hinders the free movement of paraffin single crystals, preventing them from connecting and forming a paraffin network structure. This reduces the viscosity and pour point of the crude oil, preventing wax crystal aggregation and thus achieving the purpose of anti-waxing.

4. AR-type demulsifier

AR-type demulsifiers are novel oil-soluble, non-ionic demulsifiers synthesized from alkylphenol resin (AR resin) polymerized with polyethylene oxide and polypropylene oxide. They have an HLB value of approximately 4-8 and a demulsification temperature as low as 35-45℃. The molecular structure is: AR(PO)x(EO)yH, where: EO – polyethylene oxide; PO – polypropylene oxide; AR – resin; x, y, z – degree of polymerization. In the synthesis of the demulsifier, the AR resin acts as both an initiator and a lipophilic group within the demulsifier molecule. The characteristics of AR-type demulsifiers are: small molecular size, good dissolution, diffusion, and penetration effects even when the crude oil’s pour point is above 5℃, promoting the flocculation and aggregation of emulsified water droplets. They can remove over 80% of the water from crude oil with a water content of 50%-70% within 45 minutes at temperatures below 45℃, which is unmatched by SP-type and AP-type demulsifiers.